Amorphous precipitated silica has been used as a carrier for organic liquids such as, for example, vitamin E CAS 59-02-9!, vitamin E acetate CAS 58-95-7!, choline chloride CAS 67-48-1!, liquid organic additives for rubber such as for example hexakis(methoxymethyl)melamine CAS 3089-11-0!, and various organic phase change materials, i.e., an organic material which may be repeatedly transformed from the liquid phase to the solid phase and vice versa. The foregoing listing of organic liquids is by no means exhaustive, but exemplary; many other organic liquids may be employed for sundry purposes.
Situations often arise where it is more desirable to handle solids than to handle liquids. It is nonetheless ofttimes necessary to employ liquids. A major reason for using amorphous precipitated silica as a carrier for organic liquids is that the organic liquid can be absorbed by the precipitated silica and the combination thereafter handled as a free-flowing powder.
Different amorphous precipitated silicas have different carrying capacities for organic liquids. In most instances it is desirable for the carrying capacity of the silica to be as great as reasonably possible; this permits the quantity of both materials that must be handled to be minimized. It is at the same time desirable that the mixture of amorphous precipitated silica and absorbed organic liquid contain little or no dust.
The carrying capacity may be regarded as approximately the maximum amount of organic liquid that can be absorbed by the silica such that the mixture still retains the characteristics of a free-flowing powder. As a sample of the amorphous precipitated silica absorbs an organic liquid, the mixture changes from a free-flowing state to one of a semiplastic agglomeration, with an accompanying increase in viscosity. It will be appreciated that the carrying capacity of the amorphous precipitated silica for a particular organic liquid depends upon the identities of both the amorphous precipitated silica and the liquid. Also, the transition from a free-flowing powder to a semiplastic does not involve a sharp discontinuity when viscosity is plotted as a function of organic liquid content. Standard tests using a standard organic liquid are therefore used to characterize the carrying capacity, as will be discussed in more detail below.